One of the more difficult problems associated with any borehole is to communicate measured data between one or more locations down a borehole and the surface, or between downhole locations themselves. For example, in the oil and gas industry it is desirable to communicate data generated downhole to the surface during operations such as drilling, perforating, fracturing, and drill stem or well testing; and during production operations such as reservoir evaluation testing, pressure and temperature monitoring. Communication is also desired to transmit intelligence from the surface to downhole tools or instruments to effect, control or modify operations or parameters.
Accurate and reliable downhole communication is particularly important when complex data comprising a set of measurements or instructions is to be communicated, i.e., when more than a single measurement or a simple trigger signal has to be communicated. For the transmission of complex data it is often desirable to communicate encoded analog or digital signals. These transmissions can be performed through direct wire connection between the surface and the downhole location(s) or through wireless communications techniques such as electromagnetic waves, pressure or fluid pulses, and acoustic communication.
A tubing is composed of many pipes linked together by connections. There are few nominal sizes for the outside diameter (for example 2⅞ inches, 3.5 inches or 4.5 inches). The outside diameter has a rather large tolerance which is defined by norms edited by the American Petroleum Institute. The connection between pipes, which may be called a “coupling”, comprises a thread, and a very large variety of connections exist on the present market. Most of the time, the coupling outside diameters are larger than a diameter of the pipe.
When a device, such as a sensor (temperature, pressure) or a transmitter (for example acoustic transmitter) must be secured on the pipe, such device can either be installed in a carrier (also called a mandrel) placed between two pieces of pipe (see for example, U.S. Pat. No. 7,339,494) or it can be clamped directly along the outside diameter of the pipe, using one or several mechanical collars called “clamps”. Usually, the prior art clamps are made of at least two parts which are secured together so that they can be directly installed on the tubing, without engaging the connections.
However, a tool secured outside of the tubing can be exposed to large axial loads and shock when the pipe is moving inside an open hole (whose rugged surface can generate a high friction force when dragging), or when the tool engages a liner. The liner, for example, may be a casing of smaller size located in a lower part of a well. Therefore, the liner forms an abrupt change in diameter with the upper casing. When the tool is an acoustic modem, such acoustic modem has a transceiver assembly which vibrates to introduce axial stress waves into the tubing. In this instance, the acoustic modem should be securely connected to the tubing to maximize the signal transferred from the acoustic modem into the tubing.
As discussed above, clamps are often used for attaching downhole communications tools and/or wires to a downhole pipe. Clamps are well known in the art and take the form of hinged friction collars, hinged collars with set screws, and hinged collars with dogs. See for example, U.S. Pat. No. 6,957,704.
The hinged collar described in the '704 patent has two semicircular bands which are joined at one end by a hinge. At the opposite ends from the hinge, the semicircular bands have a flange through which a bolt extends. Thus, the hinged style stop collar is attached to a pipe by spreading the semicircular bands wide enough to receive the pipe. Rotating about the hinge, the semicircular bands are closed together until a bolt can be inserted through the flanges and tightened. As the bolt tightens, the flanges are drawn closer together so as to squeeze the collar about the pipe.
Moreover, as described/shown in the '704 patent, the hinged collar with set screws also comprises two semicircular bands which together surround a pipe. In this case, however, both ends of both semicircular bands have a hinge. The hinge is made up of corresponding eyelet pieces which are joined by a pin. Thus, the collar is attached to a pipe by placing the semicircular bands on opposite sides of the pipe and mating the hinge eyelets at the ends of the bands. With the hinge eyelets properly mated, pins are inserted into the eyelets. The semicircular bands also comprise set screws which are used to tighten the collar on the pipe. The set screws extend in a radial direction through the bands toward the pipe.
Hinged collars with dogs are again made of two semicircular bands which mate with each other to extend about the circumference of a pipe. Rather than eyelets, two ends of the semicircular bands are joined by interlocking fingers. The opposite ends of the bands have flanges through which a bolt extends. As the bolt is tightened, the flanges are drawn closer together so as to squeeze the bands around the circumference of the pipe. This collar also has several dogs which extend radially through the bands to provide protrusions or bulges on the interior of the bands for engagement with the casing. As the bolt is tightened and the bands are squeezed about the circumference of the pipe, the dogs firmly engage the outer surface of the pipe.
Prior art clamps generally rely on friction to stay in position. Usually made from carbon steel, the surface finish of a pipe can vary with rust and other imperfections. When friction clamps are secured on a rusty surface, resistance to axial load pressures is lowered because rust has low shearing characteristics.
Techniques have been proposed to enhance a shear coupling between a housing of a transmitter assembly and a wall of a tubular string. For example, U.S. Pat. No. 7,595,737 discloses a transmitter assembly of an acoustic telemetry system which is shear coupled to the wall of the tubular string. To enhance the shear coupling between the housing and the wall of the tubular string, external mating surfaces of the housing and the wall may be roughened, serrated, etc. to provide increased grip therebetween.
Clamps with a hinge located on one side of the pipe have uneven distribution of the load, biased to the side of the pipe on which the bolts are located. The load is lesser on the hinge side because most of the force has been absorbed by the friction between the clamp and the pipe.
Pipe diameter varies, because tolerances for pipe diameter are large. Clamps must be capable of fitting even the largest pipe diameter. Prior art clamps contact the pipe mainly on two lines located in the center plane, placing pressure on relatively small areas of the pipe 180° from each other. The pipes, having relatively thin walls, can be deformed into an oval shape.
Despite the efforts of the prior art, there exists a need for a clamp assembly adapted to include improved contact with pipe material, even distribution of load, and more contact points with the pipe. It is therefore desirable to provide an improved clamp assembly with better load bearing, load distribution, and pipe contact features. It is to such a clamp assembly to the present disclosure is directed.